Context: There’s a migration process from `UserV1`...

# codingconventions

[miqbaldc]

Context: There’s a migration process from UserV1 to UserV2 from our shared prefs

Which one do you prefer?

1️⃣

UserV1 & UserV2 is nullable if fetched from server, but we provide a blank/default value

data class UserV1(status: String? = "", phoneNumber: String? = "", areaCode: Int? = -1)
data class UserV2(
   accountInfo: Account? = null,
   domicileInfo: Domicile? = null, 
)
data class Account(status: String? = "", phoneNumber: String? = "")
data class Domicile(areaCode: Int? = -1)

fun UserV1?.toUserV2() = UserV2(
    accountInfo = Account(status = this?.status.orEmpty(), phoneNumber = this?.phoneNumber.orEmpty()),
    domicileInfo = Domicile(areaCode = this?.areaCode ?: -1)
)
fun UserV2?.orEmpty() = UserV2()

// wrapping the whole if condition, e.g: (if a else b).orEmpty()
fun findUser() = (if (userV2?.status?.isNullOrBlank() == false) userV2 else userV1.toUserV2()).orEmpty()

2️⃣

UserV1 & UserV2 is nullable if fetched from server, and leave it null (no blank/default value)

data class UserV1(status: String? = null, phoneNumber: String? = null, areaCode: Int? = null)
data class UserV2(
   accountInfo: Account? = null,
   domicileInfo: Domicile? = null, 
)
data class Account(status: String? = null, phoneNumber: String? = null)
data class Domicile(areaCode: Int? = null)

fun UserV1?.toUserV2() = UserV2(
    accountInfo = Account(status = this?.status.orEmpty(), phoneNumber = this?.phoneNumber.orEmpty()),
    domicileInfo = Domicile(areaCode = this?.areaCode ?: -1)
)
fun UserV2?.orEmpty() = UserV2()

// call the `.orEmpty()` twice, e.g: if a.orEmpty() else b.orEmpty()
fun findUser() = if (userV2?.status?.isNullOrBlank() == false) userV2.orEmpty() else userV1.toUserV2().orEmpty()

[Tobias Berger]

if your fields are nullable, why would you fill them with placeholder values? It will just be even more of a mess if you need to handle these "empty" fields somehow. Of course you should not only adapt the default values in the constructor declaration, but also remove all the fallback values (.orEmpty() / ?: -1) in the mapping function.
Also, I'd suggest making accountInfo and domicileInfo non-null properties and using an empty object as the default if necessary. That might also save you some null handling later.